Introduction xxv Chapter 1: Objects All The Way Down 1 Kotlin: A New Programming Language 1 What is Kotlin? 2 What Does Kotlin Add to Java? 3 Kotlin is Object-Oriented 3 Interlude: Set Up Your Kotlin Environment 4 Install Kotlin (and an IDE) 4 Install IntelliJ 5 Create Your Kotlin Program 8 Compile and Run Your Kotlin Program 9 Fix Any Errors as They Appear 10 Install Kotlin (and Use the Command Line) 10 Command-Line Kotlin on Windows 10 Command-Line Kotlin on Mac OS X 11 Command-Line Kotlin on UNIX-Based Systems 12 Verify Your Command-Line Installation 12 Creating Useful Objects 13 Pass In Values to an Object Using Its Constructor 13 Print an Object with toString() 14 Terminology Update: Functions and Methods 15 Print an Object (and Do It with Shorthand) 15 Override the toString() Method 16 All Data is Not a Property Value 17 Initialize an Object and Change a Variable 19 Initialize a Class with a Block 19 Kotlin Auto-Generates Getters and Setters 20 Terminology Update: Getters, Setters, Mutators, Accessors 20 Constants Can''t Change (Sort of) 21 Chapter 2: It''s Hard To Break Kotlin 25 Upgrade Your Kotlin Class Game 25 Name a File According to Its Class 26 Organize Your Classes with Packages 27 Put Person in a Package 28 Classes: The Ultimate Type in Kotlin 31 Kotlin Has a Large Number of Types 31 Numbers in Kotlin 31 Letters and Things 32 Truth or Fiction 33 Types Aren''t Interchangeable (Part 1) 33 You Must Initialize Your Properties 34 Types Aren''t Interchangeable (Part 2) 35 You Can Explicitly Tell Kotlin What Type to Use 36 Try to Anticipate How Types Will Be Used 37 It''s Easy to Break Kotlin (Sort of) 37 Overriding Property Accessors and Mutators 37 Custom-Set Properties Can''t Be in a Primary Constructor 38 Move Properties Out of Your Primary Constructors 38 Initialize Properties Immediately 39 Try to Avoid Overusing Names 41 Override Mutators for Certain Properties 41 Classes Can Have Custom Behavior 43 Define a Custom Method on Your Class 43 Every Property Must Be Initialized 44 Assign an Uninitialized Property a Dummy Value 45 Tell Kotlin You''ll Initialize a Property Later 45 Assign Your Property the Return Value from a Function 46 Sometimes You Don''t Need a Property! 47 TYPE SAFETY CHANGES EVERYTHING 49 Writing Code is Rarely Linear 49 Chapter 3: Kotlin is Extremely Classy 51 Objects, Classes, and Kotlin 51 All Classes Need an equals(x) Method 52 Equals(x) is Used to Compare Two Objects 52 Override equals(x) to Make It Meaningful 54 Every Object is a Particular Type 56 A Brief Introduction to Null 58 Every Object Instance Needs a Unique hashCode() 59 All Classes Inherit from Any 59 Always Override hashCode() and equals(x) 61 Default Hash Codes Are Based on Memory Location 63 Use Hash Codes to Come Up with Hash Codes 63 Searching (and Other Things) Depend on Useful and Fast equals(x) and hashCode() 64 Multiple Properties to Differentiate Them in hashCode() 65 Use == over equals(x) for Speed 66 A Quick Speed Check on hashCode() 66 Basic Class Methods Are Really Important 67 Chapter 4: Inheritance Matters 69 Good Classes Are Not Always Complex Classes 69 Keep It Simple, Stupid 70 Keep It Flexible, Stupid 71 Classes Can Define Default Values for Properties 73 Constructors Can Accept Default Values 74 Kotlin Expects Arguments in Order 74 Specify Arguments by Name 74 Change the Order of Arguments (If You Need) 75 Secondary Constructors Provide Additional Construction Options 76 Secondary Constructors Come Second 76 Secondary Constructors Can Assign Property Values 77 You Can Assign null to a Property . Sometimes 79 null Properties Can Cause Problems 81 Handle Dependent Values with Custom Mutators 82 Set Dependent Values in a Custom Mutator 82 All Property Assignments Use the Property''s Mutator 83 Nullable Values Can Be Set to null! 84 Limit Access to Dependent Values 86 When Possible, Calculate Dependent Values 87 You Can Avoid Parentheses with a Read-Only Property 88 Need Specifics? Consider a Subclass 91 Any is the Base Class for Everything in Kotlin 91 { . } Is Shorthand for Collapsed Code 93 A Class Must Be Open for Subclassing 94 Terminology: Subclass, Inherit, Base Class, and More 95 A Subclass Must Follow Its Superclass''s Rules 96 A Subclass Gets Behavior from All of Its Superclasses 96 Your Subclass Should Be Different Than Your Superclass 97 Subclass Constructors Often Add Arguments 97 Don''t Make Mutable What Isn''t Mutable 98 Sometimes Objects Don''t Exactly Map to the Real World 99 Generally, Objects Should Map to the Real World 99 Chapter 5: Lists and Sets and Maps, Oh My! 101 Lists Are Just a Collection of Things 101 Kotlin Lists: One Type of Collection 101 Collection is a Factory for Collection Objects 102 Collection is Automatically Available to Your Code 104 Mutating a Mutable List 105 Getting Properties from a Mutable List 105 Lists (and Collections) Can Be Typed 106 Give Your Lists Types 107 Iterate over Your Lists 108 Kotlin Tries to Figure Out What You Mean 111 Lists Are Ordered and Can Repeat 111 Order Gives You Ordered Access 112 Lists Can Contain Duplicate Items 112 Sets: Unordered but Unique 113 In Sets, Ordering is Not Guaranteed 114 When Does Order Matter? 115 Sort Lists (and Sets) on the Fly 115 Sets: No Duplicates, No Matter What 116 Sets "Swallow Up" Duplicates 116 Sets Use equals(x) to Determine Existing Membership 116 Using a Set? Check equals(x) 119 Iterators Aren''t (Always) Mutable 119 Maps: When a Single Value Isn''t Enough 119 Maps Are Created by Factories 120 Use Keys to Find Values 120 How Do You Want Your Value? 121 Filter a Collection by . Anything 121 Filter Based on a Certain Criterion 122 Filter Has a Number of Useful Variations 123 Collections: For Primitive and Custom Types 123 Add a Collection to Person 124 Allow Collections to Be Added to Collection Properties 126 Sets and MutableSets Aren''t the Same 127 Collection Properties Are Just Collections 128 Chapter 6: The Future (In Kotlin) is Generic 129 Generics Allow Deferring of a Type 129 Collections Are Generic 129 Parameterized Types Are Available Throughout a Class 130 Generic: What Exactly Does It Refer To? 131 Generics Try to Infer a Type When Possible 132 Kotlin Looks for Matching Types 132 Kotlin Looks for the Narrowest Type 132 Sometimes Type Inference is Wrong 133 Don''t Assume You Know Object Intent 133 Kotlin Doesn''t Tell You the Generic Type 134 Just Tell Kotlin What You Want! 134 Covariance: A Study in Types and Assignment 134 What about Generic Types? 135 Some Languages Take Extra Work to Be Covariant 137 Kotlin Actually Takes Extra Work to Be Covariant, Too 137 Sometimes You Have to Make Explicit What is Obvious 137 Covariant Types Limit the Input Type as Well as the Output Type 137 Covariance is Really about Making Inheritance Work the Way You Expect 138 Contravariance: Building Consumers from Generic Types 138 Contravariance: Limiting What Comes Out Rather Than What Comes In 139 Contravariance Works from a Base Class Down to a Subclass 141 Contravariant Classes Can''t Return a Generic Type 141 Does Any of This Really Matter? 142 Unsafevariance: Learning The Rules, then Breaking Them 142 Typeprojection Lets You Deal with Base Classes 143 Variance Can Affect Functions, Not Just Classes 143 Type Projection Tells Kotlin to Allow Subclasses as Input for a Base Class 144 Producers Can''t Consume and Consumers Can''t Produce 145 Variance Can''t Solve Every Problem 145 Chapter 7: Flying Through Control Structures 147 Control Structures Are the Bread and Butter of Programming 147 If and Else: The Great Decision Point 148 !! Ensures Non-Nullable Values 148 Control Structures Affect the Flow of Your Code 149 if and else Follow a Basic Structure 150 Expressions and if Statements 151 Use the Results of an if Statement Directly 152 Kotlin Has No Ternary Operator 153 A Block Evaluates to the Last Statement in That Block 153 if Statements That Are Assigned Must Have else Blocks 154 When is Kotlin''s Version of Switch 154 Each Comparison or Condition is a Code Block 155 Handle Everything Else with an else Block 156 Each Branch Can Support a Range 157 Each Branch Usually Has a Partial Expression 158 Branch Conditions Are Checked Sequentially 159 Branch Conditions Are Just Expressions 159 When Can Be Evaluated as a Statement, Too 160 For is for Looping 161 For in Kotlin Requires an Iterator 162 You Do Less, Kotlin Does More 163 For Has Requirements for Iteration 163 You Can Grab Indices Instead of Objects with for 164 Use While to Execute until a Condition is False 167.